THE NEW WORLD MONKEYS 43 and the caudal vertebrae depend on the length of the tail. The sacrum is quadrangular, and the iliac bones are long and narrow, with a long pubic syniphysis. The entire pelvis has a cylindrical appearance. The sternum is narrow and composed of many parts, and the thorax is laterally compressed. The humerus has an entepicondylar foramen for the passage and protection of the brachial artery and median nerve in all except Brachyteles (Weber). The carpus has an os centrale. The phalanges are long and incurved, being thus suitable for an arboreal life. But the pollex is only represented by the rnetacarpal bone in Ateles. Alimentary Canal.—The tongue has no sublingua, but frenal lamellae are present. The stomach is simple, but Vrolik (217) pointed out that there is a tendency to sacculation in Ateles and Alouatta, as in the Old World Semnopithecinae. The colon is long in the Douroucoulis and Marmosets, but it is short in other forms; and the caecum is devoid of a vermiform appendix. The liver is intermediate in character between those of the Lemur oidea on the one hand, and the Catarrhini on the other. The four lobes—right and left central and right and left lateral—vary in their relative proportions. Thus the four lobes are almost equal in A teles, the lateral lobes are much larger than the central lobes in Pithecia and Midas, or there is a progressive diminution in the size of the lobes from right lateral to left lateral as in Cebus. The Spigelian and caudate lobes are well marked. And the gall-bladder is deeply recessed in the hepatic tissue. The pancreatic and common bile ducts open together into the duodenum.